Real world scenes may have contrast ratios of as much as 50,000:1 between the brightest highlights and the darkest shadows. Many existing cameras do not support HDR because of the high costs associated with HDR image acquisition under existing approaches. For example, image sensors that are capable of producing differentiating responses to a wide range of luminance levels are expensive to manufacture. Even if deployed at a high cost, a large volume of image data requiring expensive processing power to process would be generated.
Most consumer devices do not have a native HDR image acquisition capability. To approximate an HDR image, multiple non-HDR images of a scene may first be taken with different exposure settings, and may be merged in the spatial domain by image processing software. In order to determine a suitable approximate luminance level of a pixel in an output image, multiple images are used to provide a wide dynamic range of luminance on a pixel-by-pixel basis. A consumer-grade device may create the above-mentioned multiple images in the form of compressed files in a transform domain. To read out luminance levels at a specific pixel, the compressed files must undergo decompression and transformation from the transform domain to the spatial domain. Image data in the spatial domain, as derived from the compressed files, may then be merged and reconstructed into an HDR image. The HDR image may be tone-mapped, domain transformed, and compressed to produce a tone-mapped image (e.g., with 8 bits per color value such as R, G, or B color value) approximating the HDR image of a scene. These techniques require complex logic and high computation costs, and hence are difficult and expensive to be implemented in consumer-grade devices.
As a result, many existing image acquisition devices are not capable of taking advantage of the fact that an HDR image can be created by merging multiple images of the same scene.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.